diff --git a/zigrtiow/src/main.zig b/zigrtiow/src/main.zig
index 3563947..751d4d9 100644
--- a/zigrtiow/src/main.zig
+++ b/zigrtiow/src/main.zig
@@ -1,20 +1,21 @@
 const std = @import("std");
+const info = std.log.info;
 
 pub fn main() anyerror!void {
-    const image_width: usize = 256;
-    const image_height: usize = 256;
+    const image_width: isize = 256;
+    const image_height: isize = 256;
 
     const stdout = std.io.getStdOut();
 
-    std.log.info("Writing image {d}x{d}\n", .{ image_width, image_height });
+    info("Writing image {d}x{d}\n", .{ image_width, image_height });
     try stdout.writer().print("P3\n{d} {d}\n255\n", .{ image_width, image_height });
 
-    var j: usize = 0;
-    while (j < image_height) : (j += 1) {
-        var i: usize = 0;
+    var j: isize = image_height - 1;
+    while (j >= 0) : (j -= 1) {
+        var i: isize = 0;
         while (i < image_width) : (i += 1) {
             var r = @intToFloat(f32, i) / @intToFloat(f32, image_width - 1);
-            var g = @intToFloat(f32, image_height - j - 1) / @intToFloat(f32, image_height - 1);
+            var g = @intToFloat(f32, j) / @intToFloat(f32, image_height - 1);
             var b: f32 = 0.25;
 
             var ir = @floatToInt(u8, 255.999 * r);